SANTA ROSA, Calif. — The wildfires tearing through California wine country flared anew Wednesday, growing in size and number as authorities issued new evacuation orders and announced that hundreds more homes and businesses had been lost. The death toll climbed to 21 and was expected to rise higher still.

At least 3,500 homes and businesses have been destroyed since the fires started Sunday, making them the third deadliest and most destructive blazes in state history.

"We have had big fires in the past. This is one of the biggest, most serious, and it's not over," Gov. Jerry Brown said at a news conference, alongside the state's top emergency officials, who said that 8,000 firefighters and other personnel were battling the blazes and more resources were pouring in from Oregon, Nevada, Washington and Arizona.

Nearly three days after the flames ignited, firefighters were still unable to gain control of the blazes. California Department of Forestry and Fire Protection spokesman Daniel Berlant said 22 wildfires were burning, up from 17 on Tuesday.

"Make no mistake, this is a serious, critical, catastrophic event," said Ken Pimlott, chief of the department. He said the fires have burned through a staggering 265 square miles of urban and rural areas. The return of high winds and low humidity ignited ground that was parched from years of drought.

"We are literally looking at explosive vegetation," he said. "It is very dynamic. These fires are changing by the minute in many areas."

An aerial view of homes that were destroyed by the Tubbs Fire on Wednesday in Santa Rosa, Calif. At least 21 people have died in wildfires that have burned tens of thousands of acres and destroyed over 3,000 homes and businesses in several Northern California counties.

(Justin Sullivan/Getty Images)

Alexandra Sagues, 67, packs her family's belongings with her husband, Peter, as they prepare to leave their home of 19 years Wednesday in Geyserville, Calif.

(Paul Kitagaki Jr./The Associated Press)

Wine grapes are destroyed by the Tubbs Fire on Wednesday in Napa, Calif.

(Ezra Shaw/Getty Images)

Tangerines burned black by wildfires still hang on a tree in the Coffey Park neighborhood of Santa Rosa, Calif., on Wednesday.

(Robyn Beck/Agence France-Presse)

The body of a cow that died in the Atlas Fire is seen in Soda Canyon on Wednesday near Napa, Calif.

(David McNew/Getty Images)

Homes are left completely destroyed by the Tubbs Fire on Wednesday n Kenwood, Calif.

(Ezra Shaw/Getty Images)

This home, like many others in the Country Club area of Napa, Calif., was destroyed by a raging fire fed by wind on Monday. Residents were anxious to return to their homes Wednesday, but the conditions were still too dangerous.

(Randy Pench/The Sacramento Bee)

Mary Smith, 92, wears a mask while she waits in line with family members at a road block before she can be escorted by law enforcement to retrieve some personal items from her burned home in Napa, Calif.

(Randy Pench/The Sacramento Bee)

Firefighters work to contain a wildfire Wednesday on a ranch in Bennett Valley, in Sonoma County, Calif.

(Jim Wilson/The New York Times)

Firefighters gather at a briefing before another day of battling wildfires in Sonoma County, at a station in Glen Ellen, Calif.

(Jim Wilson/The New York Times)

Flames rise from a hillside east of Santa Rosa, Calif.

(Nhat V. Meyer/The Associated Press)

The main building at Paras Vinyards burns in the Mount Veeder area of Napa in California on Tuesday.

(Josh Edelson/Agence France-Presse)

Kathryn Clickner and her fiancé embrace in the front of their home in Fountaingrove, Santa Rosa, Calif., on Tuesday.

(Kent Porter/The Associated Press)

Healdsburg firefighters rest as they and other crews protected structures from a house fire in Fountaingrove, in Santa Rosa, Calif.

(Kent Porter/The Press Democrat)

A deer stands amid the destruction on a street in the Fountaingrove neighborhood of Santa Rosa, Calif., on Tuesday.

Todd McNeive and wife Adelina McNeive look for anything to salvage from their destroyed home in the Fountaingrove Village neighborhood of Santa Rosa, Calif., on Tuesday.

(Brian van der Brug/Tribune News Service)

Homes are destroyed after wildfires ripped through the Coffey Park neighborhood of Santa Rosa, Calif.

(Robyn Beck/Agence France-Presse)

A resident flees with a suitcase as fire begins to consume the Overlook Apartment building in Santa Rosa, Calif.

(Karl Mondon/The Associated Press)

As the fires grow, officials voiced concern that separate fires would merge into even larger infernos.

"These fires are literally just burning faster than firefighters can run in some situations," Emergency Operations Director Mark Ghilarducci said.

Flames have raced across the wine-growing region and the scenic coastal area of Mendocino farther north, leaving little more than smoldering ashes and eye-stinging smoke in their wake. Whole neighborhoods are gone, with only brick chimneys and charred appliances to mark sites that were once family homes.

Authorities ordered more evacuations for parts of Sonoma Valley after a blaze grew to 44 square miles.

Sonoma County Sheriff Robert Giordano said hundreds of people were still reported missing. But officials believe many of those people will be found because chaotic evacuations and poor communications over the past few days have made locating friends and family difficult.

The sheriff also expects the death toll to climb.

"The devastation is enormous," he said. "We can't even get into most areas."

Officials in Napa County say almost half the population of Calistoga was ordered to evacuate before sunrise. Officials went through the town of 5,000 people block by block, knocking on doors to warn people to leave, Napa County Supervisor Diane Dillon said.

New evacuation orders were also in place for Green Valley in Solano County.

Meanwhile in Southern California, cooler weather and moist ocean air helped firefighters gain ground against a wildfire that has scorched more than a dozen square miles.

Orange County Fire Authority Capt. Steve Concialdi said the blaze was nearly halfway surrounded and full containment was expected by Saturday, but another round of gusty winds and low humidity levels could arrive late Thursday.